lancor



Jan. 31, 1956 9 LANCQR JR I 2,733,407

GALVANOMETER STRUCTURE Filed May 21, 1954 INVENTOR.

JOSEPH H. LANCOR, JR

FIG. 2.

BY M I I ATTORNEY GALVANOMETER STRUCTURE Application May 21, 1954, Serial No. 431,481

4 Claims. (Cl. 324-97) This invention relates to improvements in the structure of galvanometers having magetizable pole pieces which are inserted into a magnetic mounting block.

A typical galvanometer of this character comprises a lightweight fine wire coil held in suspension between a pair of stretched wires or ribbons respectively anchored at opposite ends to an enclosing galvanometer case. The suspension means defines the axis of rotary motion of the coil and supports a small mirror which is generally symmetrically arranged about this axis for deflection in response to rotation of the coil. A window in the galvanometer case aligned with the mirror enables incidence and reflection of a light beam at the mirror for sensing coil displacement.

It is desirable to provide a pair of magnetizable pole pieces mounted through opposite walls of the case to define a narrow gap in the interior of the case within which the coil is located so as to increase the intensity of the magnetic flux which acts upon the coil. The magnetizable pole pieces extend outside of the case for engagement with a magnetic mounting block having slots for receiving the magnetizable pole pieces.

Co-pending applications Serial No. 386,873 and Serial No. 386,980 which were both filed on October 19, 1953, disclose galvanometers of such construction.

It is difiicult to insert such a galvanometer into a magnetic mounting block because as the pole pieces enter the magnetic field they are attracted toward the magnetic block and tend to strike the top surface of the block, rather than entering the slots where they belong. Frequently the suspension assembly is thrown out of adjustment or damaged due to the impact which results.

These difliculties are overcome in the present invention by providing non-magnetic guide means located between the magnetizable pole pieces and the base of the galvanometer for guiding the magnetizable pole pieces into the slots in the magnet so that the pole pieces or the body of the galvanometer will not be forced against other portions of the magnet due to the pull of the magnet.

In a preferred embodiment of the invention, the pole pieces are constructed from material which is easily magnetized, such as iron, and tips constructed of non-magnetizable material such as bronze are atfixed to the lower ends of the pole pieces. The tips are of sufiicient length to enter the associated slots before the magnetizable pole pieces are attracted to any great extent by the pull of the magnetic mounting block. Each tip is shaped by having an external chamfered corner and the lower edges of its front and back faces beveled so that the tips serve to guide the pole pieces easily into the slots.

Ordinarily the non-magnetic guide arrangement may be located anywhere between the magnetizable pole pieces of the galvanometer and the bottom of the galvanometer.

These and other features of the invention are described below and illustrated by the accompanying drawings, in which:

Fig. 1 is a front elevation of a galvanometer with a portion of the front wall of the case cut away;

Unite States Patent 2,733,407 Patented J an. 31,

Fig. 2 is a fragmentary side elevation showing the relationship of one tip with respect to its associated slot in the magnetic mounting block;

Fig. 3 is a perspective view showing the galvanometer partially inserted into the magnetic mounting block; and

Fig. 4 is a fragmentary view of another embodiment of a galvanometer showing the guiding means located separate from the magnetizable pole pieces of the galvanometer.

The galvanometer shown in the drawings comprises a case 10 in the form of a rectangularly sectioned box, the length of which is many times its cross sectional dimensions. The case comprises an elongated back strip 11 and two side strips 12, 13. A cover 14 slidably engages the side member 12, 13 and is held on the case byscrew 15.

An elongated coil 16 is suspended by upper and lower suspension wires 17, 18 respectively. A small mirror 19 is attached to the upper suspension wire which is anchored to a terminal post 20 whereby a beam of light may be directed through a lens 21 onto the mirror and reflected back through lens 21 for sensing deflection of the coil 16. Lens 22 serves as an alternate lens and may be used in the same manner as lens 21 when positioned opposite mirror 19.

The lower suspension wire 18 is bonded to a hook 23 which is afiixed to one end of a helical spring 24;. A fine, wire lead 25 is bonded at one end tothe hook 23, conveniently by soldering, and is carried upwardly in the case for connection to a second terminal post 26 which is located in a terminal housing 27.

A magnetic mounting block 28 serves to provide magnetic flux for the coll ct the galvanometer. Themagnetic mounting block comprises a pole 29 having positive polarity, and a pole 30 having negative polarity. They are located opposite each other and define a groove 31 into which the case 10 of the galvanometer is inserted. Slots, such as the slots 32 and 33, are provided in the magnetic mounting block for receiving the magnetizable pole pieces of the galvanometer.

A pair of magnetizable pole pieces 34, 35 are mounted through sides 12, 13 respectively of the case so as to provide a relatively narrow gap 36 within the case wherein the coil 16 is suspended, so as to increase the intensity of the magnetic flux which acts upon the coil.

The guide means for directing the magnetizable pole pieces into the slots in the magnet comprise a pair of shaped non-magnetizable tips 37 and 38 of bronze which are affixed to the lower portion of the pole pieces. The tips are preferably of the same thickness as the magnetizable pole pieces of the galvanometer, with each tip having front and back faces, such as the faces 39 and 40 of Fig. 2, which extend parallel to the length of the galvanometer case. The outer ends 41 and 42 of the tips are chamfered and the lower edges are beveled, as illustrated by the edges 43 and 44 of Fig. 2. The chamfered ends 41 and 42 and the beveled edges 43 and 44 may be rounded, if desired, instead of having flat surfaces as illustrated in the drawings.

Fig. 3 illustrates the magnetic mounting block 28 as having several adjacent pairs of slots so that a plurality of galvanometers may be mounted side by side in the same block. Two adjacent pairs of slots define a shoulder portion such as shoulders 45 and 46.

The insertion process utilizing the present invention is best described with reference to Figs. 2 and 3. The galvanometer case is inserted into the groove 31 which is defined by the poles 29 and 30 of the magnetic mounting block 28. Non-magnetic tips 34 and 35 enter the main field of magnetic flux 47 and engage their respec tive slots 32 and 33. The chamfered corners 41 and 42 and the beveled edges 43 and 44 serve to initially align the tips with respect to the slots as the case is inserted. When the magnetizable pole pieces 34 and 35 enter the main field of magnetic flux, the tips have sufficiently entered their i-r'espec tive slots so that i the magnetic pull 56f the magnetic block {28 cannot urge the 113016 pieces "of the galvanometer to snap or str ike-a'gainst-the shoulders "I prefer to affix ,the non-magneticguide-arrangements to-ther-bottomof the magnetizable pole pieces of the igalvanometer. However; in most arrangements the non- -magnetic guides-may be located-in other positions between the magnetizable pole pieces of the galvanometer iand the bottom of fthegal'vanom'eter. Fig. 4 illustrates an embodiment: ofthe inventionwherein non magnetic guides 57f and 38s are separate from r the magnetizabl'e PDlBEPlECS 34 and-35. :1 ithe zernbodi'mentsof both Figs; land 4'it is desir- -able;t-hat-,-the non-magnetic iguideipieces be of such dimensions that they are co-extensive with the magnetic -poletpiecesqof-the galvanometer -along directions transiverse -to the length of'the-galvanometer so that the guide .pieces will-fit'snugly in-thes lots in the magnetic mounting block and provide the most effective guiding action. 5 cl 1;.In a galvanometer having an elongated case 'enclosinga-suspension assembly including a deflection coil =and a-magnetrpole piece disposed adjacent the coil and projecting from the side of the case, the pole'piece being adapted to-slide' into a slot'i'n'a magnet block and hold the galvanometer' case in'placein the block, the improvementwhicheomprises a non-magnetic member fastened to-the'endf-of 'the pole piece that firste'nters the block when "it is 'slid into the slot, the non-magnetic member serving as a guide to facilitate the entry of the pole piece -ijito the "blockan'd reducing the force with which the pole piece is attracted to the block prior to'eritry.

2. Apparatus according to claim 1 having two of the pole pieces "disposed opposite each other-{both of "the pole pieces being equipped with nonmagnetic members.

3. In a case for holding a suspension galvanometer in a magnet block and having magnetic pole pieces fastened to and projecting from opposite sides of the case, the pole pieces being adapted to "slide into slots in the magnet block and hold the galvanometer in place in the block, the improvement which comprises non-magnetic members fastened respectively-to the ends of the pole pieces that first enterthe block when-the pole pieces are slid into the block, the non-magnetic membersserving as guides to facilitate'the-entry-of the pole pieces into the block and reducing the force with which the pole pieces are attracted to the block'prior to entry.

4. In a case for holding a suspension galvanometer in a magnet block and having magnet pole pieces fastened to and projecting frorn opposite sides ofthe case, the 'polerpieces-being adapted'to slide into slots in the magnet block andhold-the 'galvanometer in place in the block, the improvement which comprises non-magnetic members having crosssections substantially complementary to said-slotsfastened respectively to'opposite sides of the case between the pole pieces and the lower end of the case and in vertical alignment with the pole pieces,

the non-magnetic members serving as guides slidably received in said slots prior to and during entry of the .pole pieces into the block and serving to reduce the force with which the pole pieces are attracted to the block prior to entry.

References Cited in the file of this patent UNiTED STATES PATENTS 7 H Lintner Nov. 28, 1893 2,439,576 :MOIIOW Apr. 13, 1948 2,599,661 Richardson Iune'lO, 1952 

